1. Field of the Invention
This invention relates to the field of refractory bodies capable of surviving and protecting their contents if any under exposure to very high temperatures. More particularly it relates to such refractory bodies in the form of tubes, with one closed and one open end, used to protect thermocouples when they are used to determine the temperature of high temperature materials which would rapidly corrode the thermocouples if they were in direct contact. Still more particularly, this invention relates to such thermocouple protection tubes which are used in slagging coal gasifiers.
A slagging coal gasifier is so named because it is operated at a sufficiently high temperature to cause the mineral residues from the coal to take the form of slags. By control of temperature, the properties of the slag can be adjusted so that the slag will run down the wall of the gasifier and out the bottom, thereby permitting the gasifier to operate in a continuous manner.
2. Description of the Prior Art
Conventional thermocouple protection tubes are usually made of common and relatively low cost ceramics such as fireclay, alumina, or zirconia for low, moderately high, and very high temperature ranges respectively. These materials have proved satisfactory for most high temperature environments but are rapidly corroded by the environment of slagging coal gasifiers, with consequent damage to the thermocouples.
More specifically relevant prior art is shown in U.S. patent application Ser. No. 06/395,550 by Stephen D. Hartline filed July 6, 1982, now U.S. Pat. No. 4,435,514, the entire specification of which is hereby incorporated herein by reference. This Hartline application describes a magnesium chromite refractory material which was found to be highly resistant to chemical attack by coal slags in molten condition. We applied the teachings of this Hartline application to the manufacture of thermocouple tubes but found that the results were not always satisfactory, because of varying degrees of slag penetration into the tubes.